The present invention relates to reinforced refractories and more particularly to refractory compositions reinforced with higher amounts of metal fibers than previously possible.
Fiber reinforcement has been used for some time to improve tensile strength and the overall stress absorption capabilities of concretes. A synopsis of its development and study is provided by Haynes, H. H. "Investigation of Fiber Reinforcement of Thin Shell Concrete", Technical Note N-979. Naval Civil Engineering Laboratory, Port Hueneme, Calif., September, 1968. As background, Haynes outlines a number of studies concerning the fiber, its dimension and spacing in the field of concrete and mortar reinforcement.
The primary function of steel fibers in concrete is to inhibit the initiation and propagation of cracks in the concrete matrix. The effectiveness of these cracks arresters increases as the amount of fiber in the concrete increases. However, in instances where the fibers are added to the concrete during the mixing operation, the fiber loading has been limited to a maximum of about 2 volume percent due to difficulties experienced in mixing, handling, placing and consolidating concretes containing large numbers of fibers.
A method is disclosed in U.S. application Ser. No. 180,688 filed Aug. 25, 1980, now U.S. Pat. No. 4,339,289, for overlaying reinforced concrete in making repairs of roadways, bridge decks and the like in which a 11/2 inch thick bed of steel fibers is placed on the substratum with a bonding agent and infiltrated with a cement composition which may contain a superplasticizing agent. Using this procedure fiber loadings of 4 to 12% by volume have been possible in the thin layer of overlaying concrete.
Steel fibers have also been used in the reinforcement of refractory concretes (so-called castables), plastics and ramming mixtures. Typically they have not been used in amounts greater than 2% by volume for practical reasons. With amounts greater than 2% it has been difficult if not impossible to place and consolidate the fiber-containing refractory material into forms, molds, etc. While substantial improvements in service life have been achieved with fiber additions as low as 0.5 to 2.0%, the ultimate potential of fiber reinforcement in refractory materials has not been realized. This situation is dramatically illustrated by FIG. 1 of Romualdi, U.S. Pat. No. 3,429,094 directed to steel fiber reinforced concrete. This graph shows the effect of the spacing between fibers (in the concrete) on the strength ratio (fiber reinforced concrete/same concrete without fibers). It is seen that the experimental data points do not fall much below a fiber spacing of 0.1 inches. As discussed, this is related to the inability to mix, place and consolidate concretes containing high amounts of fibers. Thus, strength ratios of only 2.5 to 2.75 are attained. However, the non-linear nature of the strength ratio/spacing relationship promises much higher strength ratios at even smaller fiber spacings (i.e., below 0.1). These lower fiber spacings can, in theory, be obtained by incorporating larger amounts of fibers into the concrete. However, previously there existed no adequate system for doing so. Thus a need exists for a technique able to introduce higher amounts of steel fibers into a refractory composition resulting in heretofore unattainable increases in strength which will significantly increase the service life of these refractory products.